A dynamic modal of the milling of ball end milling is presented for the simulation and analyzing the influence of the milling parameters on milling in order to avoid the vibration. The milling cutter and constrains are simplified to be a system with the two modes of vibration, the modal is developed considering effective cutting area of the cutting edge and regenerative effect, which directly reflects the cutter-in and the cutter-out. The mode testing and identifying determine the equation coefficients. It is found that reducing the milling depth can improve the stability and avoid self-excited vibration milling when the depth less than the critical milling depth, the frequency of the milling system will change while changing the rotate speed of the spindle, the self-excited is prone to occur when the frequency is close to the natural frequency. The results of simulation are benefit of the milling and optimal design of the parallel machine tools.